Shear and compression wave testing and measuring device

ABSTRACT

A new location arrangement is made of a shear transducer in a transducer sonic velocity apparatus, as for core testing, in which a shear transducer is placed between or next to a contact piece and a compression transducer so that loading of the shear generator by the compression transducer is avoided. In another embodiment, both the shear and compressional transducers are at substantially the same point or in the same plane so that the time zero is the same for both the compressional and shear measurements. In another embodiment, the shear transducer surrounds, but does not contact, the compressional transducer, and both the shear and compressional transducers contact a mounting plate or platen in about the same plane so that the time zero is the same for both the compressional and shear measurements. 
     Increased shear and compressional signals can be obtained by placing an oil depending film between a shear and its corresponding compressional transducer. In another embodiment, an oil decoupling film is provided between a compressional transducer, which is surrounded by a shear transducer, and a platen or contact piece which decouples the compressional transducer from the shear transducer.

This is a continuation-in-part application of my copending applicationhaving Ser. No. 518,854, filed Oct. 29, 1974, now abandoned, which was acontinuation application of Ser. No. 322,260, filed Jan. 9, 1973, nowabandoned, which in turn was a divisional application of Ser. No.28,368, filed Apr. 14, 1970, now abandoned.

This invention relates to a new location arrangement of a sheartransducer as in a device in which a compression transducer is alsoemployed.

In one of its concepts, the invention provides a shear transducer whichcan be either a transmitter and/or a receiver which is cut from a pieceor bar of material, for example, lead zirconium titanate, and which hasthe form in one embodiment thereof of a segmented pie constructed ofpieces of the material and so arranged that when subjected to a highfrequency alternating electrical pulse, the combination of the pieces soarranged will engender a rotational torque; in a now preferred form, theshear transducer being shaped of several pie-shaped wedges or cuts orpieces arranged so that direction of polarization in all of them, lyingin a plane, as in the form of a wafer, will be the same, thus to producean important increase in torque applied, and which, when applied to,say, a cylindrical core piece, for analysis of its porosity and othercharacteristics as can be determined by sonic velocities therethrough,will give a symmetrical wave throughout the cylindrical core piece, thusgiving results which are more homogeneous and, therefore, more fullyrepresentative of the characteristics of all parts of the piece, saidshear transducer being provided in a new location arrangement in atransducer sonic velocity apparatus as for core testing next to acontact piece, that is, between a contact piece abutting an end of acore to be tested and a compression transducer, permitting to avoidloading the path of travel of any shear impulse with the compressionaltransducer, that is, the compressional transmitter and/or receiverduring shear sine wave transmission.

In a further concept of the invention, a shear transducer is formed ofpie-shaped segments bonded to the end of a mounting plate or platen andthrough an enlarged axial opening in the shear transducer a small, butthicker, compressional transducer is mounted and coupled to the mountingplate or platen.

A further concept of the invention provides a new arrangement of anyshear transducer and any compressional transducer in which in a coretester the shear transducer is placed between a contact piece and acompressional transducer.

In another concept of the invention, a ring-shaped, segmented sheartransducer surrounds, but does not contact, a smaller, but thicker,compressional transducer, and both the shear and compressionaltransducers contact the surface of a platen in the same plane so thatthe time zero is substantially the same for both the compressional andshear measurements.

In a still further concept of the invention an oil decoupling film isprovided between a compressional and a shear transducer arranged asherein described.

In still a further concept of the invention, an oil or grease decouplingfilm which decouples a compressional transducer from a shear transduceris provided between a compressional transducer and a platen arrangedsuch that the compressional transducer is surrounded by, but notcontacted with, a shear transducer and wherein the shear andcompressional transducers contact the platen in about the same plane.

The testing of materials to determine their various characteristics asby passing sonic or other impulses or vibrations therethrough is known.Thus, the determining of the velocity of shear waves and longitudinalwaves in porous media under either hydrostatic or axial loading or bothto simulate conditions as in a well, that is, in the formationsurrounding a well, has been practiced for some time. Thus, it is knownthat, depending upon the density or porosity of a material, the velocityof a sine wave or other impulse, however created therethrough, willvary. As is known, the velocity of transmission is all the greater thatthe material is more dense.

Those skilled in the art will have as background information within thescope of their knowledge the information which is evident from thefollowing references.

"Apparatus for Simultaneous Determination of Longitudinal and Shear WaveVelocities Under Pressure," Journal Scientific Instruments, 1967, Vol.44, Pages 379-381, and information in the footnote references of thearticle.

"Ultrasonic Shear-Wave Velocities in Rocks Subjected to SimulatedOverburden Pressure," Geophysics, Vol. XXVII, No. 5, October, 1962,Pages 590-598 and footnote references to the article.

"Producing Motion with Magnetostrictive and Piezoelectric Transducers,"Electrical Manufacturing, December, 1955, Pages 40-43.

U.s. pat. No. 3,213,358, Raymond G. Piety, Oct. 19, 1965.

U.s. pat. No. 3,329,931, Denis R. Tanguy, July 4, 1967.

The information of the references to the art, as shown therein, isincorporated herein by reference. Accordingly, in that which follows,the reader is assumed to be familiar with that art.

I have conceived of an arrangement for a core tester apparatus wherein ashear transmitter and/or shear receiver is placed in juxtaposition tothe contact piece or pieces between which the core to be tested isclamped.

I have also conceived of an arrangement for a core logging apparatuswherein a ring-shaped shear transducer, i.e., a shear transmitter and/ora shear receiver, surrounds, but does not contact, a compressionaltransducer, and both are positioned such that the shear andcompressional transducers contact a platen in about the same plane and,in a preferred embodiment, an oil decoupling film is provided betweenthe compressional transducer and the platen which decouples thecompressional transducer from the shear transducer.

In the prior art, as illustrated in the Steveninck article,above-mentioned, at page 380 thereof, in FIG. 3, there is illustrated adevice for measurements under hydrostatic pressure in which there isshown a shear transducer atop a longitudinal or compressionaltransducer. That is to say, the longitudinal or compressional transduceris located between the shear transducer and the contact piece. In thatarticle, it is stated that a series of experiments showed that the otherside of the shear-wave transducer must be completely free; no backingmaterial in any form should be used. Indeed, the article states at thetop of column 1 of page 380 that the shear-wave transducer must beplaced on the outside to avoid backing by any material other than air.The use of a delayed sweep, such as the Tektronix type 545, as can beused in this invention, is there set forth. The article also states thatit is clear that, although the two types of transducers are cementedtogether, there is no interference from one pair when the other pair isin use.

Nevertheless, it remains a fact that the shear transducer must apply itsshear through the longitudinal transducer which loads against thetransmission of the shear wave. According to the arrangement hereindescribed in which I have reversed the order of assembly and in apreferred embodiment of which I have provided a shear transducer asherein described, there can be obtained better definition of the shearsine wave as against the compression sine wave. In accomplishing theresults which I have obtained, it is clear that I have proceeded contrato the teaching of Steveninck, as given in the article written by himand above identified.

For those who may be unfamiliar with magnetostrictive and piezoelectrictransducers, it should be understood that a transducer, as hereindiscussed, responds to an electrical stimulus by producing a mechanicaleffect, i.e., force and motion, and, conversely, it translates amechanical stimulus into an electrical signal. Magnetostrictive andpiezoelectric transducers are discussed in the above article in"Electrical Manufacturing," Suffice to say, that, as the magnetic orelectric field impulses act upon the pieces of a shear or compressionaltransducer, as herein described, there will be a change in the physicaldimension of each of the said pieces or elements.

In my new transducer, as herein described, the shear wave signals havebeen significantly improved by reversing the order in which the shearand compressional transducers were earlier applied to the specimencontact pieces. Oscillograms made with the contact pieces face-to-faceshow the increase in "first arrival" shear wave energy to be aboutfive-fold over signals observed with the original transducer. There hasbeen little, if any, loss in compressional wave signal owing to thechange. The contact pieces of the invention are somewhat shorter thanearlier used.

Referring again to the Steveninck article, it will be noted that the twotransducers are combined by rigidly cementing the shear element to theback of the compressional element. This rigid connection is essential inSteveninck's device because of the nature of shear wave transmission.However, this design, as earlier noted, causes the mass of thecompressional element to load the shear unit, lowering resonantfrequency and reducing signal levels.

Ordinarily, as used, a core testing apparatus or transmitter assembly isencompassed within an oil bath which simulates the pressure of theformation from which a core or formation sample has been taken.

As later described, in one embodiment there is employed a film of oil orgrease between the adjacent faces of the shear and compressionaltransmitters, and, in another embodiment, there is employed an oil orgrease film in the same plane as the shear and compression transducerscontact the platen. This film of oil cannot transmit the shear energy,and, therefore, the mass of the compressional element is effectivelydecoupled from the action of the shear transducer. Nevertheless, the oilfilm provides adequate coupling for energy developed by thecompressional element. As a result, overall performance of the sonicvelocity apparatus over that of the prior art has been significantlyenhanced.

Thus, in effect, increased shear and compressional signals are obtainedin one embodiment for use in measuring the sonic velocity in coresamples by placing oil coupling films and an electrode between the shearand compressional transmitters. The shear transmitter can be cementeddirectly to the specimen contact piece and both transmitters areimmersed in oil and held against the core by a spring, as laterdescribed.

In another embodiment, an oil or grease decoupling film is placedbetween the compressional transducer and the platen. The sheartransducer is of such size as to allow the compressional transducer topass through, but not contact, the shear transducer. One end of theshear transducer is cemented to the platen and the other end of theshear transducer is cemented to the electrode. Since there is a spacebetween the compressional transducer and the shear transducer,electrical contact between the two crystals is prevented. In this waythe signal produced by the compressional transducer does not affect theshear transducer, and vice versa. However, the oil film between thecompressional tranducer and platen serves to decouple the compressionaltransducer from the shear transducer and reduces the loading effects ofthe compressional transducer when the shear transducer is in operation.

It is an object of this invention to accomplish shear and/or compressiontransducing.

It is another object of the invention to provide a new shear transducercombination.

It is a further object of this invention to apply in a new arrangement ashear transducer and a compressional transducer to a core testingapparatus.

A still further object of the invention combination is to apply a newshear transducer to the new arrangement of a shear and compressionaltransducer in a core tester.

It is a further object of the invention to obtain clear and definiteseparation of shear and compressional signals or sonic waves transmittedthrough a core, as in a core testing operation or device.

A further object of this invention is to provide a coupling between thecompressional transducer and the platen in a new arrangement.

A still further object of this invention is to provide an oil or greasedecoupling film that decouples a compressional transducer from a sheartransducer in the shear-compressional transducer combinations of theinvention.

Other aspects, concepts, objects, and the several advantages of theinvention are apparent from a study of this disclosure, the drawings,and the appended claims.

According to the invention, there is provided an apparatus for measuringcharacteristics of a core or formation sample by passing shear andcompressional waves therethrough wherein there are provided in theapparatus contact pieces for holding between them a core or formationsample to be tested and wherein at least one shear transducer is placedimmediately adjacent said contact piece. In this arrangement a shearsignal can be induced without being loaded by the compressionaltransducer.

Still further according to the invention, the shear and compressiontransducer elements are assembled in a concentric arrangement, and bothelements contact the platen in the same plane so that the time zero isthe same for both the compressional and shear measurements.

Further according to the invention, at least one oil decoupling filmand/or electrode is positioned between the shear and compressionaltransmitters or receivers or both when their positioning according tothis invention is observed.

Still further according to the invention, an oil or grease decouplingfilm is placed between a compressional transducer and the platen holdingsame in a concentric arrangement where the compressional transducer issurrounded by a shear transducer which film decouples the compressionaltransducer from the shear transducer.

According to the invention as described in the several figures of thedrawing, there can be obtained increased shear or compressional signalsthrough core samples, velocities of which can be better measured anddistinguished not only by virtue of the special structure of the sheartransmitting and/or receiving element or elements, but also by virtue ofthe arrangement of a shear transducer between the compressional elementor transducer and the core or sample or its respective contact piece.

Referring now to the figures of the drawing, in

FIG. 1 there is shown an apparatus for sonic velocity measurement as ofrock or formation samples which is adapted to simulate conditions in theformation, for example, the pressure the sample would bear were it stillin the formation and the connate water or brine it might be wetting thesame.

FIGS. 1a and 1b show in expanded manner the details of the top andbottom structures of the device which include, respectively, on the onehand the shear and compressional transmitters and on the other the shearand compressional receivers.

FIG. 1c corresponds to FIG. 1a and shows in expanded form the bottomstructure of another embodiment of the device which embodies aconcentric arrangement of the shear and compressional transducers.

FIG. 1d shows a side view of the shear and compression transducers inconcentric assembly.

FIG. 1e is a top view of FIG. 1d showing the concentric arrangement ofthe shear and compression transducers.

FIG. 2 shows in somewhat more detail details of an assembly somewhatlike that of FIG. 1a, and

FIG. 3 shows in somewhat more detail an assembly somewhat like that ofFIG. 1b, FIGS. 2 and 3 also showing electrical leads and in diagrammaticform important pieces of apparatus employed in connection therewith.

FIG. 4 shows one form of the polysegmented structure of a sheartransducer or wafer.

FIG. 5 shows the amplitude of the first break signal (downgoing pulse)produced at the shear receiving transducer by pulsing the sheartransmitting transducer when the shear transducers are placed outsidethe compressional transducers.

FIG. 6 shows the amplitude of the first break signal (downgoing pulse)produced at the shear receiving transducer by pulsing the sheartransmitting transducer when the shear transducers are placed inside thecompressional transducers and next to the contact pieces.

Referring now to FIG. 1, 1 and 2 are clamping members which are roddedtogether by several rods illustrated by rods 3 and 4. Member 1 isstationary on rods 3 and 4 and has formed within its recess 5 adapted toreceive therein contact piece 6. Clamping member 2 is provided withscrew press 7 equipped with movable recessed member 8 having recess 9therein adapted to retainingly engage contact piece 10. A core or rockspecimen 11 is held between contact pieces 6 and 10, and, in thisembodiment, is surrounded by a rubber or plastic sleeve 12 sealinglyprotecting core 11 from any fluid which may be ambient around the areaof the core. Bustle rings 13 and 14 are machined into contact pieces 6and 10.

Referring now to FIG. 1a, there are provided together with and abovecontact piece 6, a shear receiver 20, an electrode 21, a compressionalreceiver 22, a fiber washer 23, a spring 24, an insulating sleeve 25, acollar 26, and a saturant tube 27. In FIG. 1a, saturant tube 27 iswelded securely in contact piece 6. All of the elements 21 to 27 in FIG.1 having a center opening are placed around saturant tube 27 and held inplace by spring 24 which is kept under compression by collar 26. Collar26 is held in place on saturant tube 27 by a recessed set screw (notshown). Contact pieces 10 and 6 are positioned in recesses 9 and 5,respectively, and held in place by epoxy cement as shown in FIG. 1. Thecontact pieces can be made to rest against O-ring washers which arepositioned between the contact pieces and the recesses 5 and 9.Considering now FIGS. 1 and 1a, it will be seen that there can beintroduced by means of saturant tube 27 to the core sample 11, forexample, a brine solution to wet the core sample and also by means notshown applying to the brine a pressure to simulate that which thesolution would have in the pores of the sample were it still in theground. For example, if the core has been taken from a depth of 5,000feet, multiplying by the factors 0.435, which has been determined forbrine solution, it is necessary to use a brine pressure in the testingapparatus of 2175 pounds per square inch (0.435 × 5,000). The entireassembly of FIG. 1 can be placed in a pressure vessel and the formationpressure at the particular depth from which the core sample has beentaken simulated. This pressure in the example given will be about 5,000pounds per square inch. The function of the plastic sleeve 12 is nowmore readily apparent.

Referring now to FIG. 1b, there is provided below contact piece 10,shear transmitter 30, electrode 31, compressional transducer 32, fiberwasher 33, and spring 34. Spring 34 may be a leaf or coil springattached to 8 for holding the transmitter assembly against contact piece10.

In one embodiment of the invention and in its preferred form, there isprovided between electrode 31 and shear transmitter 30 an oil film.Likewise, there can be provided, according to the preferred embodimentof the invention, between electrode 21 and shear receiver 20 in FIG. 1aa similar oil film. The oil film or films function to permit motion ofthe shear receiver with respect to the compressional transducers as willbe more apparent in connection with FIGS. 2 and 3.

Referring now to FIG. 1c, which substantially corresponds to FIG. 1adescribed above, there is provided a contact piece on platen 6. Sheartransducer 20 is in the same position with respect to platen 6 asdescribed above with respect to FIG. 1a, but the hole through the centerof shear transducer 20 is larger than the hole in the previouslydescribed shear transducer. The larger hole through the center isprovided to allow insertion of a compressional transducer. The electrode21 is cemented onto the shear transducer 20. The compressionaltransducer 22 is a cylindrical crystal and thicker than the oneillustrated in FIG. 1a and also thicker than shear transducer 20. Thecompressional transducer passes through the hole in electrode 21, andtransducer 22 touches platen 6. An oil decoupling film is placed betweencompressional transducer 22 and platen 6. There is a cylindrical spacebetween compressional transducer 22 and shear transducer 20 such as toprevent electrical contacts between the two crystals. In this way thesignal produced by the compressional transducer does not affect theshear transducer and vice versa. However, the oil film betweencompressional transducer 22 and platen 6 serves as a decoupling film andreduces the loading effects of a compressional transducer when the sheartransducer is in operation.

An electrode 22' is cemented to the top of compressional transducer 22.A coiled spring 24 is positioned above compressional transducer 22 andelectrode 22'. Pipe 27 is used to supply the saturant for the core. Inthis connection, pipe 27 passes through the hole in platen 6, and, inthis particular embodiment, both the bottom platen and top platen havepipe 27 through platen 6 so that saturant fluid can be supplied fromboth ends of the core. A coiled spring 24' is used in this embodiment tosupply pressure on top of electrode 21 on top of shear transducer 20.

In FIG. 1d the outer circle is the shear transducer 20 with electrode 21cemented on top thereof. The bottom portion of crystal transducer 20 iscemented to the platen as pointed out above. A space is provided insidethe cylindrical section of shear transducer 20 through whichcompressional transducer 22 is placed. Electrode 22' is cemented to thetop of compressional transducer 22, and the oil decoupling film beingpositioned below compressional transducer 22 between the top of platen6. The oil film does not extend out beyond the outer edges ofcompressional transducer 22.

In FIG. 1e, which is a top view of FIG. 1d, there are illustrated thepie slices of shear transducer 20, the electrical insulating spacebetween the compressional and shear transducers, and the hole in thecenter through which pipe 27 is placed to supply saturant fluid to thecore under test.

In the embodiment described above in connection with FIGS. 1c, 1d, and1e, the shear and compressional transducers are separated, and one doesnot tend to load the other. The transducers are separated by a largehole which is made in the shear transducer of such size as to allow thecompressional transducer which is cylindrical to pass through the sheartransducer. In this embodiment, one end of the shear transducer iscemented to the platen, and the electrode is cemented onto the other endof the shear transducer. The compressional transducer which iscylindrical passes through the large hole in the shear transducer andpresses against the platen. An oil decoupling film is placed between thecompressional transducer and the platen which reduces the loadingeffects of the compressional transducer when the shear transducer is inoperation.

FIGS. 2 and 3 show, respectively, in exploded form, the assemblage ofFIGS. 1a and 1b, respectively, but in more detail in that the electricalequipment is diagrammatically illustrated. Thus, in FIG. 3, there isshown electrical lead lines connecting oscillator 37 to thecompressional element 32 by way of switch 35 and the electrode 31 by wayof switch 36 to ground. As shown in FIG. 3, contact piece 10 is groundedby a suitable ground as is the oscillator. In more detail now, thespring 34 holds the assembly of FIG. 3 together against contact piece 10and in order the compressional element 32 is coated with silver bearingepoxy cement, and electrode 31 is cemented to compressional element 32.Next is the oil film between electrode 31 and shear transmitter 30, thebottom side of which is coated with silver bearing epoxy and next thecontact piece 10. The element 30 and contact piece 10 are cementedtogether with silver bearing epoxy cement or resin. The segments ofshear transmitter 30 and shear receiver 20 are separated from each otherby an electrical insulating epoxy cement. By operation of switch 35 andswitch 36 together there are transmitted, usually sequentially, impulsesby way of the respective transmitters 30 and 32. Thus, usually, onesignal is produced so that only one transmitter is connected to theoscillator 37 while the remaining transmitter is disconnected from theoscillator.

Referring now to FIG. 2, electrical lead lines, respectively, connectthe compressional element 22, the electrode 21, and the shear receiver20 through switches 38 or 39 to detector and recorder 40. Oscillator 37is connected to detector and recorder 40, such as an oscilloscope, byelectrical cable 41 in order to provide synchronous operation of the twoinstruments in proper time relationship. The cementing, oil film, andcoating are as before but symmetrically positioned with respect to thecore located between contact pieces 6 and 10.

The plate electrode in both FIGS. 2 and 3 is cemented to thecompressional transducer which is an ordinary cylindrical crystal about1/10 inch thick. The shear transducer is about 1/20 of an inch thick.

Referring now to FIG. 4, there is shown a shear transducer. The arrowsshow the lining up of the pieces so that polarization of each segment orsector will be in the same direction and sense. The polarization isshown by the full arrows. The rotational motion during application ofthe field or current and return to rest position of each segment isshown by the broken double-headed arrows.

The pie-shaped crystals are portions of a rectangular block which is cutdiagonally, the rectangular edges being rounded off to form the segmentsas shown.

The several segments are electrically insulated from each other by meansof epoxy cement which holds them together. The insulation between thesegments prevents shorting out of any segment and assures that it willcontribute to producing shear forces.

Ordinarily, the electrical circuits of the invention carry oscillatorgenerator signals having a frequency in the approximate range 500 to1000 kilocycles per second, pulsed periodically to cause the crystals toengender the desired signals. In an actual operation, testing anoil-bearing formation core, a 700 kilocycle frequency was pulsed on boththe shear and compressional transducers.

When so doing, the shear wave signals were significantly improved owingto having reversed the order in which the shear and compressionaltransducers were originally applied to the specimen contact piece.Oscillograms made with the contact pieces face to face show the increasein "first arrival" shear wave energy to be about five-fold over signalsobserved with the transducers in the original or unreversed order.

In carrying out tests on this instrument, the contact pieces 10 and 6 ofFIGS. 2 and 3 were placed face to face with no core between the two.This test was used to determine time delay in the circuits andtransducer assemblies with no core present and also to determine torelative strengths of the signals detected by the receiving transducers.Of importance to this invention, the order of placement of thetransducers was reversed to that described here. It was found that withthe arrangement of placing the shear transmitter and detectortransducers adjacent the contact pieces (the compression transducersbeyond the shear transducers) that a five-fold increase in the shearsignal received at detector 40 was achieved over the conditions when thecompressional transducers were adjacent the contact pieces (the sheartransducers beyond the compressional transducers), with the same inputpulses or signals. The tests were carried out in a pressure vessel withthe transmitters and receivers under 5,000 lbs. per square inch pressurewhich simulates downhole pressures at a depth of 5,000 feet.

In making measurements using the apparatus of this invention, a 3/4-inchdiameter core is cut from a larger core obtained by well-known meansfrom a well in the Panhandle Pool, More County, Tex. The cores arecylindrical and approximately 13/8 inch long. The cores are loaded intoa Tygon sleeve with the sleeve ends being placed around the ends of thecontact pieces as shown in FIG. 1. After the core has been inserted thelower contact piece is screwed up against the core in order that thecore may be held tightly between the two end pieces. The core andapparatus of this invention are then ready for being tested in apressure vessel (not shown). The pressure vessel is approximately 3inches in inside diameter and 12 inches long with steel walls 11/2inches thick. The apparatus shown in FIG. 1 is bolted to the top endpiece of the cylindrical pressure vessel which is screwed into place asis the bottom end piece. Both end pieces are equipped with electricalleads and pressure connections with the generating electrodes goingthrough the bottom end piece and the receiving or pickup electricalleads coming out the top of the cylinder end pieces. The top cylinderend piece also has a tube connecting to tube 27 to supply internalpressure to the core as pointed out previously. The external pressure tothe core is supplied through the bottom end piece of the cylinderwherein the pressures of up to 5000 pounds per square inch are injectedaround the core and Tygon cylinder. Once the end pieces of the pressurevessel have been screwed into place and oil pressure built up to 5000pounds per square inch externally inside the pressure vessel and outsidethe Tygon tube, and 2175 pounds applied internally by injecting a brinesolution through the tube leading to the core inside the Tygon tube, theequipment is ready for testing the core at ambient temperatures.

The receiving and transmitting shear transducers are 7/8 inch indiameter. The compressional transducers are 3/4 inch in diameter and1/10 inch thick while the shear transducers are only 1/20 inch thick.The ratio of the thickness of the compressional transducers to the sheartransducers is 2:1, in order that they operate at their resonancefrequencies since the velocities of sound in the two types oftransducers have a ratio of 2:1. The receiving shear transducer differsfrom the transmitting transducer in that there is a hole placed throughthe middle of the receiving transducer in order to allow the tubecarrying the internal pressure to the core to pass therethrough withoutcoming in contact with the shear receiving transducer. The hole in theshear and compressional receivers is 3/16 inch in diameter which allowsthe 1/8 inch diameter injection tubing to pass therethrough withoutmaking electrical contact with the receiving transducers. Both sheartransducers are made up of five segments cemented together with a smallamount of epoxy cement electrically insulating the sectors from eachother. This insulation between the sectors permits each individualsector to operate by itself and allows for individual testing of eachsector to see if it is putting out or receiving energy before it is usedin this test equipment.

A high-powered pulsed oscillator is used to supply electrical pulses tothe transmitting transducers with the transmitted energy being receivedby the receiving transducers for display on the oscilloscope. Theoscillator and oscilloscope are operated synchronously in order that thedetected signals will appear at appropriate places on the oscilloscope.The individual transmitting transducers are operated separately andpulsed 200 times per second by means well known by those skilled in theelectronics art in order to get a standing image on the oscilloscope.The duration of each pulse is 5 microseconds. The voltage applied to thetransmitting transducers is 450 peak-to-peak volts. The oscillator putsout a 700 kilocycle per second frequency signal which is pulsed for 5microseconds as pointed out above.

In making tests on this equipment the relative strengths of the signalsreceived at the receiving transducers as determined by the amplitude ofthe first break on the oscilloscope of the downgoing portion of thesignal was made to determine whether or not more energy will betransmitted and received with the shear transducers placed next to thecontact pieces as shown in FIG. 3 or whether or not more energy would betransmitted and received if the compressional transducers were placednext to the contact pieces. In making this test in particular withreference to the shear signals from the shear transducer the contactpieces 10 and 6 were placed face to face with no core between the twopieces in a Tygon tube. 5000 lbs./square inch of oil pressure wasapplied to the pressure vessel as previously described. No pressure wasapplied internally since the contact pieces would allow no significantpressure to be exerted against the Tygon tube since they were in contactface to face. The oscilloscope was adjusted for voltage reading perdivision, and readings made on the scope as shown in FIGS. 6 and 7. Inthis particular oscilloscope the divisions on its face were 1 centimeteralong the horizontal and vertical axes. FIG. 5 shows the output signalfor shear signals when the compressional transducer is placed next tothe contact pieces (the shear transducers beyond the compressionaltransducers) and the shear transmitting transducer pulsed. FIG. 6 showsthe results obtained by pulsing the shear transmitting transducer whenit was placed next to the contact pieces (the compressional transducersbeyond the shear transducers) as shown in FIGS. 2 and 3. The 700 kcsignal was pulsed at 5 microseconds with 450 peak-to-peak volts andapplied only to the shear transmitting transducer as described above.Data obtained from the receiving shear transducer are shown in Table I.

                                      TABLE I                                     __________________________________________________________________________    For Shear Signals                                                             __________________________________________________________________________    With no core between contact pieces                                                            Scope    Reading on Scope                                                                        Actual                                                     Volts/Division                                                                         in Divisions                                                                            Volts                                     __________________________________________________________________________    1.                                                                              Shear signals when shear                                                      transducers are placed out-                                                   side of compressional trans-                                                  ducers         0.05     2.1       0.105                                     2.                                                                              Shear signals when shear                                                      transducers next to contact                                                   pieces         0.2      2.6       0.52                                      __________________________________________________________________________

With the compressional transducers placed next to the contact pieces andthe shear measurement taken, the adjustment on the oscilloscope was 0.05volts/division. The reading on the oscilloscope was 2.1 divisions.Multiplying these two values together gives an actual voltage output forthe shear transducer to be 0.105 volts. When the shear transducers wereplaced next to the contact pieces as shown in FIGS. 2 and 3, thevolts/division on the oscilloscope was 0.2. The actual reading on thescope during pulsing of the shear transmitting transducer was 2.6.Multiplying these two values together gives an actual voltage of 0.52for the transmitted shear signal. The amplitude read on the oscilloscopeis shown in FIGS. 5 and 6 for shear pulsing and receiving under the twoabove conditions. Dividing 0.52 by 0.105 gives a five-fold increase ofthe shear signal when the shear transducers are placed next to thecontact pieces over that for shear signals when the compressionaltransducers are placed next to the contact pieces.

Reasonable variation and modification are possible within the scope ofthe foregoing disclosure, the drawing, and the appended claims to theinvention, the essence of which is that there have been providedtransducer sonic velocity testing or measuring apparatus embodying ashear transducer and a compressional transducer wherein the order ofassembly of the shear and compressional transducers has been reversedand in one modification an oil film is employed between the providedelectrode and the compressional transducer, and, in another embodiment,an oil film is provided between the compressional transducer and theplaten or contact piece in a concentric arrangement of shear andcompressional transducers, and further that the shear transducer whichcan be used in such apparatus in a preferred embodiment is composed ofpie-shaped segments.

I claim:
 1. A transducer sonic velocity testing or measuring apparatusadapted to measure the respective velocities of rotational shear andcompressional waves passed through a sample which comprises contactpieces for holding a sample such as a formation core therebetween, arotational shear transmitter, and a compressional transmitter fortransmitting, respectively, a rotational shear and a compressional wavethrough said sample, a rotational shear receiver and compressional wavereceiver, respectively, for receiving a rotational shear and acompressional wave transmitted through said core, the apparatus beingcharacterized in that at least one of the rotational shear transducersis positioned between a compressional transducer and the contact pieceat an end of said core, and an oil decoupling film between one of theshear and one of the compressional transducers at said end.
 2. Anapparatus according to claim 1 having spring bias means for holding therotational shear transducer and its corresponding compressionaltransducer together.
 3. An apparatus according to claim 1 having meansfor supplying an electrical impulse to the rotational shear andcompressional transducers, respectively, and means for receivingtransmitted impulses or sonic waves and recording or otherwisedisplaying the same as received by the rotational shear andcompressional receivers, respectively.
 4. An apparatus which comprisescontact pieces for holding a sample such as a formation coretherebetween, a rotational shear transmitter and a compressionaltransmitter for transmitting, respectively, a rotational shear wave anda compressional wave through said sample, rotational shear wave andcompressional wave receivers, respectively, for receiving a rotationalshear wave and a compressional wave transmitted through said core, theapparatus being characterized in that at least one of the rotationalshear transducers is positioned between a compressional transducer andthe contact piece at an end of said core, and an oil decoupling filmbetween the rotational shear transducer and the correspondingcompressional transducer at said end.
 5. An apparatus according to claim4 having spring bias means for holding the rotational shear transducerand its corresponding compressional transducer together, means forsupplying an electrical impulse to the rotational shear andcompressional transducers, respectively, and means for receivingtransmitted impulses or sonic waves and recording or otherwisedisplaying the same as received by the rotational shear andcompressional receivers, respectively.
 6. A transducer sonic velocitytesting or measuring apparatus adapted to measure the respectivevelocities of rotational shear and compressional waves passed through asample which comprises contact pieces for holding a sample such as aformation core therebetween, a rotational shear transmitter and acompressional transmitter for transmitting, respectively, a rotationalshear and a compressional wave through said sample, a rotational shearreceiver and compressional wave receiver, respectively, for receiving arotational shear and a compressional wave transmitted through said core,the apparatus being characterized in that at least one of the rotationalshear transducers is positioned between a compressional transducer andthe contact piece at said end of said core, and an oil decoupling filmbetween the rotational shear and compressional transmitters, thearrangement thereby permitting including a rotational shear wave withoutloading of the compressional transducer against said rotational shearwave.
 7. A transducer sonic velocity testing or measuring apparatusadapted to measure the respective velocities of rotational shear andcompressional waves passed through a sample which comprises contactpieces for holding a sample such as a formation core therebetween, arotational shear transmitter and a compressional transmitter fortransmitting, respectively, a rotational shear and a compressional wavethrough said sample, a rotational shear receiver and compressional wavereceiver, respectively, for receiving a rotational shear and acompressional wave transmitted through said core, the apparatus beingcharacterized in that one of the rotational shear transducers and acompressional transducer are both in contact in the same plane with thecontact piece at an end of said core so that the time zero issubstantially the same for both the compressional and shearmeasurements, and an oil decoupling film between the compressionaltransducer and the contact piece at said end which decouples thecompressional transducer from the shear transducer.
 8. An apparatusaccording to claim 7 having spring bias means for holding the rotationalshear transducer and its corresponding compressional transducertogether.
 9. An apparatus according to claim 7 having means forsupplying an electrical impulse to the rotational shear andcompressional transducers, respectively, and means for receivingtransmitted impulses or sonic waves and recording or otherwisedisplaying the same as received by the rotational shear andcompressional receivers, respectively.
 10. An apparatus which comprisescontact pieces for holding a sample such as a formation coretherebetween, a rotational shear transmitter and a compressionaltransmitter for transmitting, respectively, a rotational shear wave anda compressional wave through said sample, rotational shear wave andcompressional wave receivers, respectively, for receiving a rotationalshear wave and a compressional wave transmitted through said core, theapparatus being characterized in that at least one of the rotationalshear transducers surrounds, but does not contact, the compressionaltransducers and both are in contact in the same plane with the contactpiece at an end of said core so that the time zero is substantially thesame for both the compressional and shear measurements, and an oildecoupling film between the compressional transducer and the contactpiece at said end which decouples the compressional transducer from theshear transducer.
 11. An apparatus according to claim 10 having springbias means for holding the rotational shear transducer and itscorresponding compressional transducer together, means for supplying anelectrical impulse to the rotational shear and compressionaltransducers, respectively, and means for receiving transmitted impulsesor sonic waves and recording or otherwise displaying the same asreceived by the rotational shear and compressional receivers,respectively.
 12. A transducer sonic velocity testing or measuringapparatus adapted to measure the respective velocities of rotationalshear and compressional waves passed through a sample which comprisescontact pieces for holding a sample such as a formation coretherebetween, a rotational shear transmitter and a compressionaltransmitter for transmitting, respectively, a rotational shear and acompressional wave through said sample, a rotational shear receiver andcompressional wave receiver, respectively, for receiving a rotationalshear and a compressional wave transmitted through said core, theapparatus being characterized in that one of the rotational sheartransducers is formed of pie-shaped segments bonded to a contact pieceand through an enlarged axial opening in the shear transducer a smaller,but thicker compressional transducer is mounted and coupled to thecontact piece at an end of said core, and an oil decoupling film betweenthe compressional transducers and the contact piece at said end whichdecouples the compressional transducer from the shear transducer.
 13. Anapparatus according to claim 12 wherein the shear transducer is aring-shaped segmented transducer surrounding, but not contacting, thecompressional transducer.
 14. A transducer sonic velocity testing ormeasuring apparatus adapted to measure the respective velocities ofrotational shear and compressional waves passed through a sample whichcomprises contact pieces for holding a sample such as a formation coretherebetween, a rotational shear transmitter, and a compressionaltransmitter for transmitting, respectively, a rotational shear and acompressional wave through said sample, a rotational shear receiver andcompressional wave receiver, respectively, for receiving a rotationalshear and a compressional wave transmitted through said core, theapparatus being characterized in that at least one of the rotationalshear transducers is positioned next to the contact piece at an end ofsaid core, and an oil decoupling film below one of the compressionaltransducers at said end which decouples the compressional transducerfrom the shear transducer.
 15. An apparatus according to claim 14 havingspring bias means for holding the rotational shear transducer and itscorresponding compressional transducer together, means for supplying anelectrical impulse to the rotational shear and compressionaltransducers, respectively, and means for receiving transmitted impulsesor sonic waves and recording or otherwise displaying the same asreceived by the rotational shear and compressional receivers,respectively.